1. Technical Field
The present invention relates to a piezoelectric device and a method for manufacturing the same. Particularly, the invention relates to a piezoelectric device including a piezoelectric resonator and a circuit element connected thereto, which are stacked in their thickness direction, and a method for manufacturing the piezoelectric device.
2. Related Art
There is known a structure of a piezoelectric oscillator having an oscillation circuit (e.g. an integrated circuit such as an IC), as shown in FIGS. 17 and 18. Specifically, a piezoelectric oscillator 1 shown in FIG. 17 includes a package 2 for accommodating a piezoelectric resonator element 4. The package 2 has stepped inner surfaces to arrange the piezoelectric resonator element 4 on an upper side and an IC 3 on a lower side in the single package 2. Meanwhile, a piezoelectric oscillator 1a shown in FIG. 18 includes a package 2a with an H-shaped structure for accommodating the piezoelectric resonator element 4, where the piezoelectric resonator element 4 and the IC 3, respectively, are accommodated in different cavities. The piezoelectric oscillators structured as above have superiority for further miniaturization and their structures can satisfy a recent demand for smaller electronic devices.
Meanwhile, in each of the piezoelectric oscillators 1 and 1a having the above structure, both of the IC 3 and the piezoelectric resonator element 4 are mounted in the single package 2 or 2a. Even if only one of the piezoelectric resonator element 4 and the IC 3 is found to be defective in its manufacturing process, the entire piezoelectric oscillator including both elements needs to be disposed.
Given that situation, there has been proposed a piezoelectric oscillator, as in JP-A-2004-180012. FIG. 19 schematically shows a structure of a piezoelectric oscillator lb disclosed in the foregoing literature. The structure thereof allows miniaturization and elimination of waste associated with handling of defects in its manufacturing process. The oscillator 1b basically includes the IC 3, a wiring substrate 6 for mounting the IC 3 thereon, a connecting member 7, and a piezoelectric resonator 5 mounted on the wiring substrate 6 by the connecting member 7. On a first surface of the wiring substrate 6 are disposed a terminal (bonding pad) 6b used for mounting the IC 3 and a terminal (connecting pad) 6a used for arranging the connecting member 7. On a second surface thereof is disposed a mounting terminal 6c used for mounting the piezoelectric oscillator 1b on a substrate of another device or the like. Additionally, the IC 3 mounted on the wiring substrate 6 is subjected to potting using a molding member (insulating resin) 8 to protect the IC 3 and a metallic wire 9 for mounting the IC 3 from moisture, contamination, shock and other problems.
JP-A-2004-180012 is an example of related art.
The piezoelectric oscillator disclosed in the above example thereof can be miniaturized, as well as the piezoelectric resonator and the IC can be individually disposed if any defect occurs therein.
However, in the above piezoelectric oscillator, it is only the molding member that can protect the IC. Thus, there is a concern that moisture (water) entering from a thin portion of the molding member or a boundary portion between the molding member and the components covered by the molding member can badly affect the IC or any other metal member thereinside. Moisture adhered on an electrode or the like inside the molding member changes electrical resistance, which can cause a problem such as a deviation of an oscillation frequency.
On a surface of a lid of the piezoelectric resonator, there are carved indications (markings) representing specifications thereof, such as an oscillation frequency and a manufacturing lot number. The markings are important for visual confirmation of a product identity. However, when the piezoelectric oscillator is entirely covered by the molding member as above, the lid surface is also inevitably covered thereby. As a result, in the piezoelectric oscillator as a finished product, it is impossible to confirm the markings provided on the lid of the piezoelectric resonator.